ABSTRACT Suspended sediment export dynamics are poorly understood in mountainous regions, as highlighted by the large scatter in the relationship between flow rate and suspended sediment concentration. This study examines how isolating surface runoff from flow rate during flood events can improve the understanding of hydrosedimentary dynamics in two small Mediterranean badland watersheds of the Draix‐Bléone observatory (Laval, 0.86 km 2 and Brusquet, 1.07 km 2 ). These catchments differ markedly in vegetation cover (32% and 87%, respectively), defined as the percentage of area covered by vegetation. Hydrograph decompositions were determined using high‐frequency, temperature‐corrected specific conductance signal. A total of 83 flood events (2015–2023) and 105 flood events (2013–2023) were analysed in the Laval and Brusquet catchments, respectively. Results show that surface runoff is the primary driver of suspended sediment mobilisation. Using surface runoff rate instead of flow rate as a predictor significantly improves the power–law relationship between suspended sediment yield and event runoff volume at the flood scale (coefficient of determination R 2 which increases from 0.5 to 0.6 in Laval and from 0.3 to 0.6 in Brusquet). Results show that seasonal variability persists in this relationship, with higher suspended sediment yield in summer than in winter for the same event runoff volume. This may reflect reduced transport capacity of surface runoff during winter, or progressive sediment source depletion over the year. The densely vegetated Brusquet catchment exhibits markedly lower surface runoff rates (18‐fold reduction) and suspended sediment yield (117‐fold reduction) compared to the sparsely vegetated Laval catchment. These contrasts likely result from enhanced infiltration, reduced soil erodibility and sediment trapping by vegetation. Overall, this study emphasises the necessity of separating flow components to better identify and prioritise hydrosedimentary processes and their variability in highly erodible watersheds.
Fischer et al. (Fri,) studied this question.